1. Field of Invention
This invention relates to improvements in automotive clutches and, in particular, to an improved heat shield.
2. Brief Statement of the Prior Art
The typical automotive clutch has a clutch disk which is attached to the drive shaft and positioned between the flywheel and a pressure plate that is bolted to the flywheel. The pressure plate includes a pressure ring which is resiliently biased to frictionally capture the clutch disc between the pressure ring and the flywheel.
The earliest versions employed pressure rings formed of gray or ductile cast iron. However, the high mass and weight of cast iron creates unacceptable inertia, rendering cast iron pressure rings unsuitable for high speed engines and performance vehicles. This unsuitability has lead to the development of aluminum pressure rings.
Aluminum, however, loses structural strength at temperatures of about 435.degree. F. and melts at about 1,200.degree. F. Consequently, aluminum pressure plates need protection against the high frictional heat and peak temperatures generated in automotive clutches. Sliding of the clutch generates surprisingly large quantities of heat which must be dissipated without overheating the clutch components, or suffer the consequential warping or destruction of the pressure ring and other clutch plate components.
Aluminum pressure rings have been protected by plasma coatings of bronze or steel approximately 0.02 to 0.125 inch thick, or by attaching a steel ring (heat shield) to the frictional surface of the pressure ring.
These attempts have not been notably successful, particularly in performance vehicles where high engine speeds and considerable frictional heat is generated. In such applications, a delicate balance must be maintained between dissipation of the heat by transfer from the steel heat shield to the aluminum pressure ring without exceeding the useful operating temperature of the pressure ring and associated pressure plate components such as the clutch springs and the like.